How important is cam selection on this build?
How important is cam selection on this build? I have a 440 inch mast 305 headed engine. 11.3:1, E85, air to air, Twin 6766 precisions. Only looking for 12 to 1300 rwhp. Figuring 15 to 18lbs of boost being that the engine made close to 800 n/a. Cam that is in it is a big solid roller 270 281@ .050 .780 lift. Was thinking maybe because I'm not trying to get every last HP out of it I might try the cam that's in it before ordering a turbo specific cam. Any thoughts?
I understand...yup I guess it did come off that way. My last street car made 1400 with a procharger big block and that was in the late 90s so this needs to be faster than that car. I was just trying to say I'm not trying to max out the combo. If I was the turbos would be bigger, I would just order the right cam and the HP goal would be much higher. Sorry for misunderstanding the reply.
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From: Norn Iron
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Verdad Gallardo That is what I was thinking. But I can afford to lose some spooling with these small turbos on 440 inches. The question would be what kind of power loss would it be and could it be made up by working the turbo a little harder being that I'm not trying to max out the combo or would the valve events just make the losses unsurmountable?
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From: Norn Iron
I'm sure it probably could....but dont underestimate the effects of a poor cam choice on a turbo build.
I can only comment on a couple of cars from direct experience, both 4cyl.
First was over 20 years ago, turbo mini where I decided to try a sort of mid range n/a cam on it.
It basically turned it into a screamer, virtually no power below 4000rpm, came on boost around 5k, but pulled strong to over 8k.
It didnt exhibit in any way the same characteristics of the cam as it would in a n/a engine.
I swapped back to a milder cam, and I could easily drive anywhere from 1500rpm, it spooled much earlier and still pulled hard to 8k.
The fast road type spec n/a cam just killed it completely.
More recently a friends Subaru, he chose the drag spec Kelford cams...and whilst it did make good power, it needed to be revved to 8500-9000rpm to go, dropped off badly between gears, and made crap power below 6000rpm because of lack of spool.
We changed housings, manifolds, turbos all in an attempt to make it spool better.
In the end after other problems associated with surviving at 9k, he changed to one spec milder with the cams.
Suddenly it would make full boost at 4800rpm, was far nicer and torquier to drive everywhere and still happy to go to 8500rpm when needed...although you just didnt need to. Boost recovery was also far better too.
The bigger cams were just **** everywhere, car ran faster with less boost too, and it also made boost far easier.
As said, dont understimate the hurt a poor cam choice can cause all round, even if yes you might still be able to make a big headline number.
I can only comment on a couple of cars from direct experience, both 4cyl.
First was over 20 years ago, turbo mini where I decided to try a sort of mid range n/a cam on it.
It basically turned it into a screamer, virtually no power below 4000rpm, came on boost around 5k, but pulled strong to over 8k.
It didnt exhibit in any way the same characteristics of the cam as it would in a n/a engine.
I swapped back to a milder cam, and I could easily drive anywhere from 1500rpm, it spooled much earlier and still pulled hard to 8k.
The fast road type spec n/a cam just killed it completely.
More recently a friends Subaru, he chose the drag spec Kelford cams...and whilst it did make good power, it needed to be revved to 8500-9000rpm to go, dropped off badly between gears, and made crap power below 6000rpm because of lack of spool.
We changed housings, manifolds, turbos all in an attempt to make it spool better.
In the end after other problems associated with surviving at 9k, he changed to one spec milder with the cams.
Suddenly it would make full boost at 4800rpm, was far nicer and torquier to drive everywhere and still happy to go to 8500rpm when needed...although you just didnt need to. Boost recovery was also far better too.
The bigger cams were just **** everywhere, car ran faster with less boost too, and it also made boost far easier.
As said, dont understimate the hurt a poor cam choice can cause all round, even if yes you might still be able to make a big headline number.
I'm sure it probably could....but dont underestimate the effects of a poor cam choice on a turbo build.
I can only comment on a couple of cars from direct experience, both 4cyl.
First was over 20 years ago, turbo mini where I decided to try a sort of mid range n/a cam on it.
It basically turned it into a screamer, virtually no power below 4000rpm, came on boost around 5k, but pulled strong to over 8k.
It didnt exhibit in any way the same characteristics of the cam as it would in a n/a engine.
I swapped back to a milder cam, and I could easily drive anywhere from 1500rpm, it spooled much earlier and still pulled hard to 8k.
The fast road type spec n/a cam just killed it completely.
More recently a friends Subaru, he chose the drag spec Kelford cams...and whilst it did make good power, it needed to be revved to 8500-9000rpm to go, dropped off badly between gears, and made crap power below 6000rpm because of lack of spool.
We changed housings, manifolds, turbos all in an attempt to make it spool better.
In the end after other problems associated with surviving at 9k, he changed to one spec milder with the cams.
Suddenly it would make full boost at 4800rpm, was far nicer and torquier to drive everywhere and still happy to go to 8500rpm when needed...although you just didnt need to. Boost recovery was also far better too.
The bigger cams were just **** everywhere, car ran faster with less boost too, and it also made boost far easier.
As said, dont understimate the hurt a poor cam choice can cause all round, even if yes you might still be able to make a big headline number.
I can only comment on a couple of cars from direct experience, both 4cyl.
First was over 20 years ago, turbo mini where I decided to try a sort of mid range n/a cam on it.
It basically turned it into a screamer, virtually no power below 4000rpm, came on boost around 5k, but pulled strong to over 8k.
It didnt exhibit in any way the same characteristics of the cam as it would in a n/a engine.
I swapped back to a milder cam, and I could easily drive anywhere from 1500rpm, it spooled much earlier and still pulled hard to 8k.
The fast road type spec n/a cam just killed it completely.
More recently a friends Subaru, he chose the drag spec Kelford cams...and whilst it did make good power, it needed to be revved to 8500-9000rpm to go, dropped off badly between gears, and made crap power below 6000rpm because of lack of spool.
We changed housings, manifolds, turbos all in an attempt to make it spool better.
In the end after other problems associated with surviving at 9k, he changed to one spec milder with the cams.
Suddenly it would make full boost at 4800rpm, was far nicer and torquier to drive everywhere and still happy to go to 8500rpm when needed...although you just didnt need to. Boost recovery was also far better too.
The bigger cams were just **** everywhere, car ran faster with less boost too, and it also made boost far easier.
As said, dont understimate the hurt a poor cam choice can cause all round, even if yes you might still be able to make a big headline number.
I have ordered cams from Tick perf and Thompson motorsports. Both times the cams were @ my door in about 2 weeks. I understand your delima not wanting to wait but I would if it meant getting the rite combo the 1st time around vs who knows what.
Thanks for the reply. I really want a cam and I don't mind waiting 2 weeks as long as I know the ball is rolling and I'm not just wasting time unnecessarily.
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Joined: Nov 2003
Posts: 13,616
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From: Norn Iron
I wasnt doing anything dramatic. Mine's still quite mild albeit I moved to a solid roller. But I had very specific idle/emissions related wants that meant I didnt want to take any chances with the cam, but for most part I'm quite happy with it.
Now knowing I met the emissions tests I needed to with ease I may consider stepping up to something with a bit more duration as I'd be fairly sure I have room to do so and still pass the yearly tests.
But even with the current cam, at a guess when at max effort it's probably in the 1100-1200hp range. I'd just like a little more rpm's at the top end.
Now knowing I met the emissions tests I needed to with ease I may consider stepping up to something with a bit more duration as I'd be fairly sure I have room to do so and still pass the yearly tests.
But even with the current cam, at a guess when at max effort it's probably in the 1100-1200hp range. I'd just like a little more rpm's at the top end.
I wasnt doing anything dramatic. Mine's still quite mild albeit I moved to a solid roller. But I had very specific idle/emissions related wants that meant I didnt want to take any chances with the cam, but for most part I'm quite happy with it.
Now knowing I met the emissions tests I needed to with ease I may consider stepping up to something with a bit more duration as I'd be fairly sure I have room to do so and still pass the yearly tests.
But even with the current cam, at a guess when at max effort it's probably in the 1100-1200hp range. I'd just like a little more rpm's at the top end.
Now knowing I met the emissions tests I needed to with ease I may consider stepping up to something with a bit more duration as I'd be fairly sure I have room to do so and still pass the yearly tests.
But even with the current cam, at a guess when at max effort it's probably in the 1100-1200hp range. I'd just like a little more rpm's at the top end.
